cross one's fingers

[cross one's fingers] {v. phr.} 1a. To cross two fingers of one hand for good luck.

Mary crossed her fingers during the race so that Tom would win.

1b. or [keep one's fingers crossed] {informal} To wish for good luck.

Keep your fingers crossed while I take the test.

2. To cross two fingers of one hand to excuse an untruth that you are telling.

Johnny crossed his fingers when he told his mother the lie.